In general, a GPS satellite utilizing a low-power direct-sequence spread spectrum (DSSS) signal transmits two types of signals, namely an L1 signal having a carrier frequency of 1574.42 MHz and an L2 signal having a carrier frequency of 1227.60 MHz. A modernized GPS additionally utilizes two commercialized signals, namely an L2c signal having a carrier frequency of 1227.60 MHz and an L5 signal having a carrier frequency of 1176.45 MHz.
Most beam formers for a GPS antenna employing conventional multiple antenna elements require accurate GPS arrival angle information in order to effectively receive a GPS signal. Since the electric power of a GPS signal is far lower than the high noise power level and the high interference signal electric power, it is quite difficult to estimate accurate GPS arrival angle information.
For the purpose of estimating a GPS arrival angle, there have been used different arrival angle estimation algorithms such as the Multiple Signal Classification (MUSIC) (referred to as “prior art 1” for the sake of convenience) and the Estimation of Signal Parameter via Rotational Invariance Techniques (ESPRIT) (referred to as “prior art 2” for the sake of convenience).
While the conventional arrival angle estimation algorithms are superior in arrival angle estimation performance, they have serious problems in estimating a GPS arrival angle. More specifically, prior to despreading, the GPS electric power remains far lower than the interference or noise power level. This makes it impossible to estimate the GPS arrival angle. If an arrival angle is estimated after despreading, the estimated arrival angle includes both a GPS arrival angle and an interference arrival angle.